C2-b857246and two mutable derivatives: c2-m881058Pand c2-m881058Yand control of their variegated phenotypes --Michael G. Muszynski and Peter A. Peterson A variegated (colored to colorless) kernel, C2-b857246, was rescued from a 1984 c2 isolation plot (C2/C2 x c2/c2) containing many elements including Cy, En, Uq, Ac and Dt (MNL 60:2). This variegated phenotype was heritable upon outcrossing to c2/c2 testers and segregated 1/4 colored:1/4 variegated:1/2 colorless as a male. When used as a female, the 2 doses of C2 make identification of the variegated kernels more difficult and therefore that class is usually less than 25% and the colored class greater than 25% by the same amount, on a per ear basis. The phenotype and inheritance seem to suggest that the mutability does not reside at C2 but that the C2 locus and perhaps other genes on 4L were being lost via a chromosomal breakage event.

This was proven by linking C2 to 3L carrying Sh2 with a translocation and the heterozygote was then crossed by and on a c2 sh2 tester. All the colorless sectors on the variegated kernels from the outcross ears were also sh2 indicating the loss of both markers.

Figure.

Therefore, this mutant is designated C2-b for C2 breaker. System tests indicate that this mutant does contain many Cy and En but neither show a correlation with the occurrence of breakage. This breakage may be under control of a previously undefined element.

Two mutable derivatives have been isolated from this mutant.

c2-m881058P: An exceptional spotted kernel (2-5 a-b) was found on an ear segregating colored, variegated and colorless. The kernel (c2-m/c2) was selfed and outcrossed several times to c2/c2 testers. The spotting phenotype was heritable and segregated 45 spotted:19 colorless from the self and 3 spotted:5 colorless from the outcrosses. This mutant allele was designated c2-m881058P and seems to be controlled by two independently segregating functional elements. The spotted kernels from the outcrossed ears segregated for three distinct phenotypes: 1 high (6-8 aa-d):1 low (2-6 aa-b):1 extreme low (1-3 aa-a). It may be that each of the two independent regulators causes a different spotting pattern in this c2-m allele and both regulators acting together elicit a third spotting phenotype. This can be verified by further testing.

c2-m881058Y: Another exceptional spotted kernel (5 b-c) was found on an ear segregating colored and colorless from C2-b857246. This mutant was found to be heritable, designated c2-m881058Y and also seems to be under control of two independently segregating regulators. The spotting phenotype is heavy (5-7 a-c) with occasional (1%-14%) low (1-4 aa-a) spotted kernels appearing. This lower spotting phenotype may be due to a change of state of the c2-m allele or to changes to one or the other or both independent regulators.

A study of the relation of c2-m881058P and c2-m881058Y to each other and to C2-b857246 is in progress. Also, studies on the cause and heritability of the lower spotting patterns and system tests are in progress.


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